The pathophysiologic mechanism in pertussis infection involves production of nitric oxide (NO) by an inducible nitric oxide synthase. A similar mechanism may exist in asthma. Nitric oxide breaks down into nitrate and nitrite in the blood and is excreted in the urine. We plan to measure NO in the breath, and nitrite in serum and urine, from patients with pertussis infection, asthma, and several other clinical disease states.